A cylinder block of a car or a truck (vehicle) is an integrated structure including cylinders of a reciprocating engine and often some or all of their associated surrounding structures (such as coolant passages, intake and exhaust passages and ports, and crankcase, etc.). The term engine block is often used synonymously with cylinder block.
Various main parts of an engine (such as cylinders, cylinder heads, coolant passages, intake and exhaust passages, and crankcase) are distinct assemblies; these assemblies may be instantiated as discrete pieces that are bolted together. Such construction was very widespread in the early decades of the commercialization of internal combustion engines (1880s to 1920s), and it is still sometimes used in certain applications where there is an advantage (especially for very large engines, but also some small engines). However, it is no longer the normal way of building most petrol engines and diesel engines, because for any given engine configuration, there are more efficient ways of designing for manufacture (and also for maintenance and repair). These generally involve integrating multiple machine elements (assemblies) into one discrete part, and doing the making (such as casting, stamping, and machining) for multiple elements in one setup with one machine coordinate system (of a machine tool or other piece of manufacturing machinery). This yields lower unit cost of production (and/or maintenance and repair). Today most engines for cars, trucks, buses, tractors, and so on are built with a fairly highly integrated engine block (cylinder block or block).
An oil-jet device is a device that is configured to spray oil to a piston assembly (such as a bottom portion of the piston assembly) of an engine block. The oil received by the piston assembly (from the oil-jet device) cools (removes heat from) the piston assembly during a combustion phase of engine-block operation. Other names for the oil-jet device are a piston-cooling nozzle or a system for cooling and lubricating the piston assembly in an internal combustion engine. During engine operation, some of the heat resulting from fuel combustion is absorbed by the piston assembly, causing an undesirable temperature rise. Without adequate heat transfer away from the piston assembly, the carbon deposits may be increased on the piston assembly. One way to reduce this excess heat is through use of the oil-jet device.